1. Field of the Invention
The invention pertains to the field of hearing protection. More particularly, the invention pertains to hearing protection using an artificial ear structure.
2. Description of Related Art
FIG. 1 shows a hearing protection system with talk-through, in the form of a headset 13 worn by a user 14. The headset has a right earcup 1 and a left earcup 2, which serve to reduce the ambient noise level heard by the user 14. Such protection systems are typically used in high-noise environments such as aircraft carrier decks, factories, etc. In order that the user 14 retain some ability to hear what is going on around him, microphones 3 and 4 feed a reduced amount of external sound to the user 14 through amplifiers 5 and 6, which power audio transducers 7 and 8. The amplifiers 5 and 6 can include various features known to the art, such as filtering, volume limiting or equalizing, etc. The audio transducers can be speakers or piezoelectric or magnetic transducers in earplugs (wired or wireless), as is known to the art.
FIG. 2 shows a talk-through earcup of the prior art in more detail, with FIG. 6 showing a section of the earcup along the lines 6-6 of FIG. 2. The point here is that typical prior art talk-through systems use a microphone 23 coupled to the outside of an earcup 21 through a hole or tube 20. The microphone 23 is sealed in a small chamber 24 so that the sound doesn't get into the earcup 21 volume. A resilient pad 22 seals the earcup around the pinna of a user's ear, as is common in most around-the-ear type earphones.
“Artificial ears” are used as objective measuring apparatus to measure sound levels, as for example for frequency response, sensitivity and distortion measurements on earphones. They enable electroacoustical measurements on either insert earphones or headphones to be carried out under well-defined acoustical conditions, which are of great importance for the comparability of different designs and the reproducibility of measurements.
International Telecommunications Union standard ITU-T P.57 (November 2005) defines a standard for artificial ears. The geometry of Type 3.4 artificial ears (“Pinna simulator—simplified”) is shown in FIG. 8/P.57 of the standard (page 16).
Studies, such as “Sound transmission to and within the human ear canal”, Hammershøi and Møller, J. Acoust. Soc. Am. 100 (1) (July 1996), have shown that recordings using a microphone in a blocked human ear canal retain the acoustic timing cues and directional dependence needed for accurate localization. The concha geometry is needed to simulate human ear response, regarding localization, while the ear canal geometry is not. The blocked canal recordings are frequency equalized when played back for the user to compensate for the ear canal, speaker, microphone, amplifier, and other responses to provide the proper frequency response at the user's ear canal.